Wet peroxide oxidation of chlorophenols

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Water Research 39 (2005) 795–802 www.elsevier.com/locate/watres

Wet peroxide oxidation of chlorophenols Vero´nica Garcı´ a-Molinaa, Marta Lo´pez-Ariasa, Magdalena Florczykb, Esther Chamarroa, Santiago Esplugasa, a Departament d’Enginyeria Quı´mica i Metallurgia, Universitat de Barcelona, Martı´ i Franque`s 1, 08028 Barcelona, Spain Department of Chemistry, Technology of Chemistry, Inorganic Chemistry and Electrochemistry, Silesian University of Technology in Gliwice, Strzody 9, 44-100 Gliwice, Poland

b

Received 14 May 2004; received in revised form 4 November 2004; accepted 21 December 2004

Abstract This study evaluates the application of Wet Peroxide Oxidation (WPO) for the treatment of solutions containing 4chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP). These compounds are of special interest due to their high toxicity and low biodegradability. WPO is included in the Advanced Oxidation Processes, which are technologies based on an initial formation of hydroxyl radicals that further oxidize the organic matter. The influence of some operating conditions such as temperature, dosage of hydrogen peroxide and initial concentration of the chlorophenols was studied in absence of a catalyst. The results of this study prove that 4-CP and 2,4-DCP can be completely removed from wastewaters by means of WPO. Total Organic Carbon (TOC) and 4-CP removals of 72.3% and 100%, respectively, were achieved working at 100 1C with 2.5 mL of H2O2 and an initial concentration of 500 ppm of 4-CP after 90 min of reaction. Under the same conditions but with an initial concentration of 500 ppm of 2,4-DCP a TOC removal of 59% and a complete removal of the target compound were achieved. r 2005 Elsevier Ltd. All rights reserved. Keywords: Wet peroxide oxidation; Advanced oxidation processes; 4-chlorophenol and 2,4-dichlorophenol

1. Introduction Over the last years the need to restore contaminated sites to avoid further risks to the environment has promoted the development of effective methods for Chlorophenols (CPs) removal. Advanced Oxidation Abbreviations: AOPs, advanced oxidation processes; WPO, wet peroxide oxidation; 4-CP, 4-chlorophenol; 2, 4-DCP, 2, 4dichlorophenol; CP(s), chlorophenol(s); TOC, total organic carbon Corresponding author. Tel.: +34 93 402 1290; fax: +34 93 402 1291. E-mail addresses: [email protected] (V. Garcı´ a-Molina), [email protected] (S. Esplugas).

Processes (AOPs) appear to be a promising field of study, since the organic components that are thermodynamically unstable to the oxidation are eliminated and not transferred from one phase to another (PeraTitus et al., 2004). AOPs were defined in 1987 by Glaze (Glaze et al., 1987) as ‘‘near ambient temperature and pressure water treatment processes which involve the generation of hydroxyl radicals in sufficient quantity to effective water purification’’. Hydroxyl radical is traditionally thought to be the active specie responsible for the destruction of pollutants (Peyton and Glaze, 1988; Glaze and Kang, 1989; Haag and Yao, 1992; Braun et al., 1993). AOPs include several techniques some of which being Ozonation, Fenton, photo-Fenton, Photocatalysis and

0043-1354/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2004.12.007

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Wet Oxidation. These processes have shown promising results either for the complete mineralization of organic compounds or for their transformation into less complex structures, which are more biodegradable (Al-Hayek and Dore´, 1990; Trapido et al., 1997; Herrmann et al., 1999). Among these technologies Supercritical Water Oxidation (SCWO), Subcritical Oxidation or Wet Oxidation (WO) and Wet Peroxide Oxidation (WPO) are of special interest. These processes differ from the rest of the AOPs not only in terms of operating conditions but also in the concentration of the pollutants present in the wastewater. They are used mainly for concentrated wastewaters in order to allow auto thermal operation, and thus a reduction in the operating costs (Catrinescu et al., 2003). SCWO takes place above the critical point of water (TX375 1C and PX22:1 MPa) (Ding et al., 1996) and WO engages with oxidation at a temperature range of 125–300 1C and pressures of 0.5–20 MPa. The use of oxygen as oxidizing agent is common to WO and SCWO processes. There is also one more process which involves oxidation with hydrogen peroxide and which uses temperatures and pressures both below the critical point of water, i.e., WPO (Debellefontaine et al., 1996). Some articles relating the degradation of phenol or derivatives by catalytic WPO have been published recently (Barrault et al., 1998; Valange et al., 1999; Catrinescu et al., 2003; Garriazo et al., 2003; Rodrı´ guez et al., 2004), however, data regarding the degradation of CPs by means of this technique is scarce. WPO processes were developed in order to decrease the running cost of Wet Oxidation, which is efficient under severe temperature and pressure conditions. The first attempt was to use a homogeneous catalyst (transition metal salts or hydrogen peroxide) in order to promote the oxidation with oxygen at lower temperatures or/and pressures. The second attempt consisted of using hydrogen peroxide instead of molecular oxygen as oxidizing agent and this lead to the development of a similar process, WPO (Debellefontaine et al., 1996). According to the mechanistic pathway for the wet oxidation system suggested by Li et al. (1991) and taking into account that the mass transfer problems of the oxygen from the gas to the liquid phase are avoided, the reactions involved in the WPO process can be described as follows: (1) OH radicals formation: The radical formation reaction occurs when the hydrogen peroxide decomposes generating hydroxyl radicals ðHO Þ (1). The decomposition of the hydrogen peroxide takes place on the surface of the reactor and other heterogeneous or homogeneous species (M) present in the system. Due to the fact that in this study a stainless steal reactor was used, it can be suggested that the metal ions contained in

the surface of the reactor play an important role in the hydroxyl radical initial formation. H2 O2 þ M ! 2 HO :

(1)

According to this reaction, one way to improve the efficiency of the process, thus, lowering operating costs, would be the use of a heterogeneous catalyst. Complete removal of phenol by catalytic WPO at mild operating conditions has been reported when using iron-based catalysts (Catrinescu et al., 2003; Garriazo et al., 2003; Gue´lou et al., 2003; Mei et al., 2004; Sotelo et al., 2004). Some other metal catalysts, such as zeolites containing Cu, Zn and Al have shown as well promising results for the WPO of phenol (Valange et al., 1999) (2) Chain reactions and oxidation of the organic compounds: At this stage of the reaction mechanism, the organic compounds are oxidized into less complex molecules by means of the hydroxyl radical. (3) Final reactions: The chain reactions end when the hydroperoxide formed during the chain reactions reacts with the organic compounds yielding the formation of alcohols (2) or when it decomposes to ketones and eventually acids (3). ROOH þ RH ! 2 ROH ðalcoholÞ;

(2)

ROOH ! Ketones ! Acids:

(3)

These scissor reactions continue until the formation of acetic and formic acid, which are more difficult to oxidize and have a longer existence time. These lowweight organic acids will be eventually converted to end products (CO2, H2O y). CPs were selected for this study because most of them are toxic and hardly biodegradable. They make up a particular group of priority toxic pollutants listed by the US EPA in the Clean Water Act (Keith and Telliard, 1979; Hayward, 1999; EPA, 2002) and by the European Decision 2455/2001/EC (2001). Their persistence in the environment is due to their chlorinated nature (Takeuchi et al., 2000) and they are considered to act as uncouplers of oxidative phosphorylation (Terada, 1990). Due to their numerous origins they can be found in ground waters, wastewater and soils (Wegman and Van den Broek, 1983) and even in the trophic chain of places with very low pollution levels (Paasivirta et al., 1980; WHO, 1989).

2. Methods and materials 2.1. Lab-scale experiments WPO reactions were carried out in a high-pressure tank reactor Autoclave Eng., model EZE-SEAL, with a capacity of 300 mL and supplied by IBERFLUID S.A.

ARTICLE IN PRESS V. Garcı´a-Molina et al. / Water Research 39 (2005) 795–802

P (7) (6)

(4)

Cooling Water

(5) (3) S

T (2)

(1)

Fig. 1. Wet peroxide oxidation equipment: (1) power supply, (2) digital controller (Temperature and Stirring Speed), (3) heater, (4) stirrer, (5) reactor, (6) samples extraction, (7) gas draining.

(Spain). The reaction cell is made of stainless steel ALSI 316 and due to a split ring pair with 6 screws the reactor is capable of working under severe conditions of pressure (max. 227 bar at 454 1C). The reactor is equipped with a heating jacket made of ceramic elements, a cooling system and an agitation system (electric motor, maximal working rate of 3000 r.p.m.). The experimental equipment also consists of an electronic controller that allows the control of both temperature and stirrer (IBERFLUID S.A. Spain). Fig. 1 shows a scheme of the experimental equipment used to carry out the WPO reactions. WPO reactions start with the preparation of CP (4-CP and 2,4-DCP) solutions and the addition of the oxidizing agent, hydrogen peroxide. Solutions containing 500 and 1000 ppm of CP were used in this study. On the other hand, the concentrations of hydrogen peroxide used were 1500, 3750 and 7500 ppm. For each reaction, 200 mL of the solution containing the CP and the hydrogen peroxide were introduced into the reactor. After this, the reactor was closed, the cooling water pump was turned on and the temperature and stirrer speed (700 rpm) were programmed in the controller. Once the selected temperature was reached, the system reacted for 90 min and during this period of time several samples were withdrawn from the reactor. The reactor was then cooled down and a last sample was taken in order to predict possible variations during the cooling down period.

2.2. Reactants and analytical methods The reactants used in this study, i.e., 4-CP, 2,4-DCP and hydrogen peroxide (30% w/v) were supplied by Panreac Quimica, S.A. (Spain). Samples were analyzed for Total Organic Carbon (TOC), pH and High Performance Liquid Chromatography (HPLC). TOC was analyzed by means of a Shimadzu 5055 TOC analyzer. HPLC was used to identify and quantify both CPs and for the detection of some intermediates of the

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reaction. HPLC was supplied by Waters Corporation (MA, USA), the column used was a TR-016059 supplied by Tecknokroma S. Coop. C. Ltd (Barcelona, Spain) with a length of 250 mm and an inner diameter of 4.6 mm. The mobile phase used was a mixture of acetonitrile (Panreac Quimica, S.A., Spain) and water in proportion of 40:60% in volume, acidified to a pH 3 by the addition of phosphoric acid (Panreac Quimica, S.A., Spain). The wavelength used in the detector was 267.3 nm. In addition, samples containing possible intermediates were prepared and their retention times were compared with the intermediates of the reactions in order to identify them.

3. Results and discussion 3.1. Blank experiments WPO reactions were planned to be carried out under high temperature (4100 1C) making inevitable the existence of a preheating period, in which the temperature of the reactor increases from room temperature to the temperature of the reaction. Blank experiments are necessary because during the preheating period the solution is under high temperature and changes in its properties and composition are likely to happen. These experiments were conducted without oxidizing agent and they consisted of introducing different concentrated (from 300 to 1000 ppm) solutions of 4-CP and 2,4-DCP in the reactor and heating it up to 200 1C. Samples were withdrawn from the reactor when its temperature reached 100, 130, 150, 175 and 200 1C. From these experiments it was proved that 4-CP solutions were not affected by the increase of the temperature when working in the range previously mentioned. In Fig. 2a, it can be observed that the TOC remained constant throughout these experiments. However, when working with 2,4-DCP some changes were observed: the TOC and the amount of 2,4-DCP decreased with the temperature for all the different concentrated solutions (see Fig. 2b). This could indicate that the dichlorophenol was being degraded as a result of the increase of the temperature. However, the pH remained constant during the experiments and 2,4-DCP was the only compound observed in the HPLC (the only peak present in the chromatograms belonged to the 2,4DCP). Moreover, the last sample taken from the reactor, once it was cooled down until 20 1C, presented the same concentration as the initial sample. These facts together showed that there is no reaction or degradation of the 2,4-DCP but instead, a mass transfer of the target compound from the liquid phase to the gas phase. The results of these blank experiments as for the TOC measured are shown in Fig. 2.

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798 650

425

TOC (ppm)

TOC (ppm)

550 450 350 250 150

325 225 125 25

20

40

60

(a)

80 100 120 140 160 180 200

1000 ppm 600 ppm

900 ppm 500 ppm

800 ppm 400 ppm

20

40

60

(b)

Temperature (°C)

1000 ppm

700 ppm 300 ppm

80 100 120 140 160 180 200

Temperature (°C) 900 ppm 500 ppm

600 ppm

800 ppm 400 ppm

700 ppm 300 ppm

(a)

80 60 40

0

17

32

47

62

77

92

20 107 152

Time (min) 1000 ppm 4-CP 1000 ppm 2,4-DCP Temperature

500 ppm 4-CP 500 ppm 2,4-DCP

100

4.5

80 3.5 60 2.5

40

1.5

(b)

0

17

32

47

62

77

92

20 107 152

Temperature (°C)

100

pH

70 60 50 40 30 20 10 0

Temperature (°C)

TOC removal (%)

Fig. 2. TOC (ppm) vs. temperature (1C). Experiments carried out heating solutions containing chlorophenol in absence of oxidizing agent. (a) 4-CP results, (b) 2,4-DCP results.

Time (min) 1000 ppm 4-CP 1000 ppm 2,4-DCP Temperature

500 ppm 4-CP 500 ppm 2,4-DCP

Fig. 3. (a) TOC removal and pH evolution (b) during the wet peroxide oxidation of solutions containing 1000 and 500 ppm of 4-CP and 2,4-DCP at 100 1C and with 1 mL of hydrogen peroxide.

3.2. WPO reactions of solutions containing 4chlorophenol and 2,4-dichlorophenol The main objective of this experimental research was to evaluate if 4-CP and 2,4-DCP could be degraded by means of WPO. Once this was checked, the influence of some operating conditions such as the temperature, dosage of hydrogen peroxide and initial concentration of CP during the WPO was studied. In addition, a rough estimation of the operating costs was undertaken.

3.2.1. Influence of the initial concentration of CP, evolution of the pH and intermediate compounds Solutions with two different concentrations i.e., 500 and 1000 ppm of the target compounds were prepared. These high concentrations were selected for this experimental research because wet oxidation processes are reactions accompanied by a release of energy (Debellefontaine et al., 1996) and, therefore, in order for the process to be energy self-sufficient, the chemical oxygen demand (COD) of the waste should be high. Several authors have reported an optimum value between 10 and 20 kg/m3 of COD in the entry stream (Verenich, 2003). WPO reactions were carried out at 100 1C of operating temperature and with three different amounts

of hydrogen peroxide 5, 2.5 and 1 mL, meaning a concentration in the reactor of 1500, 3750 and 7500 ppm, respectively. From the results, it was observed that the highest concentrated solutions presented a lower TOC removal. In fact, with 1 mL of hydrogen peroxide and with a initial solution containing 500 ppm of 4-CP the final TOC removal was 69.5% whereas a TOC removal of 29.8% was achieved when working with an initial solution of 1000 ppm of 4-CP. The same occurred with the solutions containing 2,4-DCP since a final TOC removal of 24.8 and 55.1 were observed when working with an initial concentration of 1000 and 500 ppm, respectively. In Fig. 3a the TOC removal of experiments at 100 1C, with a dose of 1 mL of hydrogen peroxide and different initial concentrations of 4-CP and 2,4-DCP are represented. According to these results it can be concluded that when working with an initial concentration of 1000 ppm the oxidizing agent is consumed within the first 30 min of the reactions, since from that moment until the end of the reaction the values of the TOC remained constant. As for the evolution of the pH throughout the reaction, it was observed that its values decreased from an initial value between 4 and 5 until a final value close to 2 (Fig. 3b). This can be explained taking into account the formation of low molecular weight acids, which are

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experiments showed a complete or nearly complete 4-CP removal after 90 min of reaction, it has to be noticed, that the abatement was faster the higher the temperature of the reaction. Fig. 4 shows the CP and TOC removals during the WPO reactions carried out at 100 and 130 1C with 5 mL of H2O2 and 1000 ppm of CPs.

the compounds typically formed before the total mineralization occurred. In addition, organic intermediates were identified from the samples withdrawn from the reactor at different times. Phenol, benzoquinone and hydroquinone appeared to be the most relevant intermediates of the process. However, the reaction pathways of the mechanism are still under study.

3.2.3. Influence of the dosage of hydrogen peroxide during the WPO reactions To study the influence of the dosage of oxidizing agent added to the system in the WPO process, reactions were carried out maintaining the rest of the operating conditions constant and varying the amount of hydrogen peroxide. Dosages of 1, 2.5 and 5 mL of H2O2 were added to the solution (200 mL), meaning thus, a concentration of 1500, 3750 and 7500 ppm of hydrogen peroxide, respectively, at the beginning of the reactions. Wet oxidation reactions were conducted at 100 1C with an initial concentration of both CPs of 1000 ppm. The values of the TOC and CPs removals after 90 min of reaction can be observed Figs. 5 and 6. These figures show that as the dosage of oxidizing agent increase a higher TOC removal is achieved. As for the CPs removals, when working with 4-CP almost a complete removal was achieved even with the lowest amount of peroxide. On the other hand, 2,4-DCP solutions showed a nearly complete removal of the target compound when

3.2.2. Influence of the operating temperature during the WPO reactions In order to study the influence of the temperature and taking into account the results of the study of the influence of the preheating period, the selected temperatures when working with 2,4-DCP were 100 and 130 1C, whereas when working with 4-CP the operating temperatures were 100, 130 and 160 1C. The chosen initial concentration of the pollutant in the solution was 1000 ppm and the doses of hydrogen peroxide added in the reactor were 2.5 and 5 mL (involving a concentration of 3750 and 7500 ppm, respectively). The results for CP and TOC removal after 90 min of reaction (without including the pre-heating period) are shown in Table 1. The first conclusion that can be drawn is that an increase in the operating temperature is correlated with an increase in the TOC removal. As for the CP removals it can be concluded that in all the experiments, complete removals of the target compounds were achieved within 90 min of reaction. However, even thought all these

Table 1 TOC and CP removals at the end of the wet peroxide oxidation reactions carried out at 100, 130 and 160 1C with different dosages of peroxide (2.5 and 5 mL) and an initial concentrations of the chlorophenols of 1000 ppm Operating temperature

WPO of 4-CP solutions

WPO of 2,4-DCP solutions

100 1C

130 1C

160 1C

100 1C

130 1C

2.5 mL H2O2

TOC removal (%) CP removal (%)

70 100

80 100

78.6 100

58.5 98.3

75.4 100

5 mL H2O2

TOC removal (%) CP removal (%)

75.9 100

84.6 100

86.8 100

72.1 100

75.5 100

80

Removal (%)

100

80

Removal (%)

100

60 40 20 0

40 20 0

0

(a)

60

20

40

60

80

100

120

Time (min) 100°C TOC removal 100°C 4-CP removal

130°C TOC removal 130°C 4-CP removal

0

(b)

20

40

60

80

100

120

Time (min) 100°C TOC removal 100°C 2,4-DCP removal

130°C TOC removal 130°C 2,4-DCP removal

Fig. 4. TOC and CP removals of wet peroxide oxidation reactions carried out at 100 and 130 1C and with 5 mL of H2O2 of solutions containing (a) 1000 ppm of 4-CP and (b) 1000 ppm of 2,4-DCP.

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800

100

Removal (%)

Removal (%)

100 80 60 40 20

80 60 40 20

0 1

(a)

2.5

0

5

Hydrogen peroxide (mL)

1

(b)

4-CP

TOC

2.5

5

Hydrogen peroxide (mL) 2,4-DCP

TOC

Fig. 5. TOC and CP removals versus dose of hydrogen peroxide after 90 min of wet peroxide oxidation at 100 1C and three dosages of peroxide (1, 2.5 and 5 mL). (a) 1000 ppm of initial concentration of 4-CP. (b) 1000 ppm of initial concentration of 2,4-DCP.

100

80

Removal (%)

Removal (%)

100

60 40 20

80 60 40 20

0

0 1

(a)

2.5

5

Hydrogen peroxide (mL) TOC

1

(b)

2.5

5

Hydrogen peroxide (mL)

4-CP

TOC

2,4-DCP

Fig. 6. TOC and CP removals versus dose of hydrogen peroxide after 90 min of wet peroxide oxidation at 100 1C and three dosages of peroxide (1, 2.5 and 5 mL). (a) 500 ppm of initial concentration of 4-CP. (b) 500 ppm of initial concentration of 2,4-DCP.

3.2.4. Operating costs and optimal experimental conditions In order to estimate which are the most suitable operating conditions to carry out WPO of solutions containing CPs, a rough analysis of the operating costs was carried out. Two aspects influence directly the operating costs of the process, i.e., the amount of hydrogen peroxide and the energy consumed to reach and maintain the desired temperature. The price of the hydrogen peroxide (30% w/v) used in these experiments was 13.60 euros/L and the price of the kw-h is 0.0816 euros (in Spain). The power of the heater was 700 W during the preheating period, which lasted on average 12.76, 18.96 and 26.71 min when the temperature of the reaction was 100, 130 and 160 1C, respectively. The estimation of the energy needed to maintain the temperature of the reactor was made taken into account the convection losses of the system. These losses were calculated using a convection coefficient of 50 W/m2K, a contact area of 2.73  103 m2 and being the experiment time 90 min. The calculation of these operating costs under the conditions of the experiments leads to the conclusion that the costs related to the heating system

90

TOC removal (%)

working with 2.5 and 5 mL, whereas with 1 mL of peroxide the removal of 2,4-DCP was 74.4%.

85 80 75 70 65 2

2.5

3

3.5

4

4.5

Operating costs (euro) 100°C 1 mL H2O2

130°C 2.5 mL H2O2

160°C 2.5 mL H2O2

100°C 2.5 mL H2O2

130°C 5 mL H2O2

160°C 5 mL H2O2

100°C 5 mL H2O2

Fig. 7. TOC removal vs. Operating costs. Wet peroxide oxidation of solutions containing 500 ppm of 4-CP. Reaction duration 90 min.

are much higher than the costs related to the consumption of the hydrogen peroxide. Thus, in order to avoid high operating costs, the temperature of the reaction should not be too high. In order to determine the most suitable operating conditions for the experiments carried out with an initial concentration of 500 ppm of 4-CP, the operating costs have been roughly analyzed. In Fig. 7, the operating

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costs are depicted in front of the TOC removal achieved by each one of these reactions. It can be noticed, that if the operating temperature is 100 1C, an increase in the dosage of H2O2 involved a high increase in the TOC removal but a slight increase in the operating costs. In addition, an increase in the temperature from 130 to 160 1C did not show a high improvement in the TOC removal but a high increase in the costs. This leads to the conclusion that the optimal operating conditions might be between 100 and 130 1C and in the case of carrying out the reaction at 100 1C, the dose of hydrogen peroxide should be high enough to achieve a good performance as for TOC removal.

4. Conclusions After carrying out wet peroxide oxidations (WPOs) at different operating conditions, varying temperature and dosage of hydrogen peroxide, and with different initial concentrations of 4-chlorophenol and 2,4-dichlorophenol, the following conclusions are suggested:

 WPO appears to be a promising technology for the



   

removal of chlorophenols (CPs) from wastewaters since complete removal of the target compound was achieved when working under not so severe conditions of temperature (100 1C, 2.5 mL of H2O2). Experiments carried out with different dosages of hydrogen peroxide i.e., oxidizing agent, showed that an increase in the dosage of hydrogen peroxide was correlated to an increase in the TOC and CP removal, especially when working with the lowest temperature (100 1C). The study of the operating temperature showed that an increase in the operating temperature while maintaining the rest of the operating conditions resulted in an increase in TOC and CP removals. WPO reactions were slower when higher the initial concentration of the CP. Some intermediates of the reaction such as phenol, hydroquine and benzoquinone were identified during this research. However, the exact pathways of the reaction has not yet been identified. Temperature appeared to have a much higher influence in the operating costs than the dosage of hydrogen peroxide.

Acknowledgements Authors are grateful to Spanish Ministry of Education and Culture (CICYT project PPQ2002-00565) for funds received to carry out this work.

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References Al-Hayek, L., Dore´, M., 1990. Oxidation des phe´nols par le peroxide d’hydroge`ne en milieu aqueux en pre´sence de fer supporte´ sur alumine. Water Res. 24, 973–982. Barrault, J., Bouchoule, C., Echachoui, K., Frini-Srasra, N., Trabelsi, M., Bergaya, F., 1998. Catalytic wet peroxide oxidation (CWPO) of phenol over mixed (Al-Cu)-pillared clays. Appl. Catal. B: Environ. 15, 269–274. Braun, A.M., Jacob, L., Oliveros, E., do Nascimento, C.A.O., 1993. Up-scaling photochemical reactions. In: Volman, D., Hammond, G.S., Neckers, D.C. (Eds.), Advances in Photochemistry, Vol. 18. Wiley, New York, pp. 235–313. Catrinescu, C., Teodosiu, C., Macoveanu, M., Miehe-Brendle´, J., Le Dred, R., 2003. Catalytic wet peroxide oxidation of phenol over Fe-exchanged pillared beidellite. Water Res. 37, 1154–1160. Debellefontaine, H., Chakchouk, M., Foussard, J.N., Tissot, D., Striolo, P., 1996. Treatment of organic aqueous wastes: wet air oxidation and wet peroxide oxidation. Environ. Pollution 92 (2), 155–164. Ding, Z.Y., Frisch, M.A., Li, L., Gloyna, E.F., 1996. Catalytic oxidation in supercritical water. Ind. Eng. Chem. Res. 35, 3257–3279. EC Decision 2455/2001/ED, 2001 of the European Parliament and of the Council of November 20, establishing the list of priority substances in the field of water policy and amending Directive 2000/60 Ec (L331 of 15-12-2001). EPA, 2002. http://www.scorecard.org. web site visited on December 2002. Garriazo, J.G., Guelou, E., Barrault, J., Tatiboue¨t, J.M., Moreno, S., 2003. Catalytic wet peroxide oxidation of phenol over Al–Cu or Al–Fe modified clays. Appl. Clay Sci. 22, 303–308. Glaze, W.H., Kang, J.W., 1989. Advanced oxidation processes. Description of a kinetic model for the oxidation of hazardous materials in aqueous media with ozone and hydrogen peroxide in a semibatch reactor. Ind. Eng. Chem. Res. 28, 1573–1587. Glaze, W.H., Kang, J.W., Chapin, D.H., 1987. The chemistry of water treatment processes involving ozone, hydrogen peroxide and UV-radiation. Ozone: Sci. Eng. 9, 335–352. Gue´lou, E., Barrault, J., Fournier, J., Tatibouet, J.-M., 2003. Active Iron species in the catalytic wet peroxide oxidation of phenol over pillared clays containing iron. Appl. Catal. B: Environ. 44 (1), 1–8. Haag, W.R., Yao, C.C.D., 1992. Rate constants for reaction of hydroxyl radicals with several drinking water contaminants. Environ. Sci. Technol. 26, 1005–1013. Hayward, K., 1999. Drinking water contaminant hit-list for US EPA. Water 21, September–October, 4. Herrmann, J.M., Matos, J., Disdier, J., Guillard, Ch., Laine, J., Malato, S., Blanco, J., 1999. Solar photocatalytic degradation of 4-chlorophenol using the synergistic effect between titania and activated carbon in aqueous suspension. Catalysis Today 54, 255–265. Keith, L.H., Telliard, W.A., 1979. Priority pollutants: a prospective view. Environ. Sci. Technol. 13 (4), 416–424. Li, L., Peishi, C., Earnest, F.G., 1991. Generalized kinetic model for wet oxidation of organic compounds. AIChE J. 37, 1687–1697.

ARTICLE IN PRESS 802

V. Garcı´a-Molina et al. / Water Research 39 (2005) 795–802

Mei, J.G., Yu, S.M., Chen, J., 2004. Heterogeneous catalytic wet peroxide oxidation of phenol over delaminated Fe-TiPILC employing microwave irradiation. Catal. Commun. 5 (8), 437–440. Paasivirta, J., Sarkka, J., Leskijarvi, T., Roos, A., 1980. Transportation and enrichment of chlorinated phenolic compounds in different aquatic food chains. Chemosphere 9 (7–8), 441–456. Pera-Titus, M., Garcı´ a-Molina, V., Ban˜os, M.A., Gime´nez, J., Esplugas, S., 2004. Degradation of chlorophenols by means of advanced oxidation processes: a general review. Appl. Catal. B: Environ. 47 (4), 219–256. Peyton, G.R., Glaze, W.H., 1988. Destruction of pollutants in water with ozone in combination with ultraviolet radiation. 3. Photolysis of aqueous ozone. Environ. Sci. Technol. 22, 761–767. Rodrı´ guez, E.V., A´lvarez, P.M., Rivas, F.J., Beltra´n, F.J., 2004. Wet peroxide oxidation of atrazine. Chemosphere 54, 71–78. Sotelo, J.L., Ovejero, G., Martı´ nez, F., Melero, J.A., Milieni, A., 2004. Catalytic wet peroxide oxidation of phenolic solutions over a LaTi1xCuxO3 perovskite catalyst. Appl. Catal. B: Environ. 47 (4), 281–294. Takeuchi, R., Suwa, Y., Yamagishi, T., Yonezawa, Y., 2000. Anaerobic transformation of chlorophenols in methano-

genic sludge unexposed to chlorophenols. Chemosphere 41, 1457–1462. Terada, H., 1990. Uncouplers of oxidative phosphorylation. Environ. Health Perspect. 87, 213–218. Trapido, M., Hirvonen, A., Veressinina, Y., Hentunen, J., Munter, R., 1997. Ozonation, ozone/UV and UV/H2O2 degradation of chlorophenols. Ozone: Sci. Eng. 19 (1), 75–96. Valange, S., Gabelica, Z., Abdellaoui, M., Clacens, J.M., Barrault, J., 1999. Synthesis of copper bearing MFI zeolites and their activity in wet peroxide oxidation of phenol. Microporous Mesoporous Mater. 30, 177–185. Verenich, S., 2003. Wet oxidation of concentrated wastewaters: process combination and reaction kinetic modelling. Lappeenranta (Finland). Acta Universitatis Lappeenrataensis 151. Ph.D. Thesis, Lappeenranta University of Technology. ISBN 951-764-739-5, ISSN 1456-4491. Wegman, R.C.C., Van den Broek, H.H., 1983. Chlorophenols in river sediment in The Netherlands. Water Res. 17 (2), 227–230. WHO (1989) World Health Organization. Environmental health criteria for chlorophenols other than pentachlorophenol. Supplement. Draft, July 31.